1. Field of the Invention
The present invention relates to a miter saw capable of adjusting the angle of a circular saw blade in relation to its base and the angle of the circular saw blade in relation to a contact surface of a fence fixed to the base.
2. Description of the Related Art
Conventional miter saws include a base for supporting a workpiece, a cutter blade portion for rotatably supporting a circular saw blade, and a supporting unit for pivotably supporting the circular saw blade about a pivoting shaft that is substantially parallel to the axis of the circular saw blade. The supporting unit can be inclined with respect to the base so that the angle formed by the side surfaces of the circular saw blade and the top surface of the base can be adjusted.
Further, if the miter saw is provided with a turntable along with the base for supporting a workpiece, the turntable is coupled with the supporting unit so that the angle of the side surfaces of the circular saw blade in relation to the top surface of the base can be adjusted.
Further, when the angle of the side surfaces of the circular saw blade can be adjusted with respect to the contact surface of the fence fixed to the base, a support for pivotably supporting the cutter blade portion is coupled with the turntable rotatably provided on the top surface of the base so that the support can rotate about the rotational axis of the turntable.
The user of the miter saw can cut the workpiece supported on the top surface of the base in a slanting direction by adjusting the angle of the side surfaces of the circular saw blade in relation to the top surface of the base. And the user can cut a workpiece at a slant in relation to the side surface of the workpiece opposing the contact surface of the fence in a vertical direction by adjusting the angle of the side surfaces of the circular saw blade in relation to the contact surface of the fence. The user performs these adjustments while referencing graduated scales integrally provided on the supporting unit and the base or turntable for indicating degree of tilt and degree of rotation. Hence, the user of this type of miter saw can be aware of the inclination angle and rotation angle by viewing the graduated scales. However, it is not easy to learn the angles of inclination and rotation instantaneously. Further, due to space restrictions, there is a restriction on the number of angle values that can be inscribed on the graduated scales. Hence, the user cannot easily learn the current angles of inclination and rotation instantaneously for angular values other than those inscribed on the graduated scales, leading to a potential drop in work efficiency.
Japanese unexamined patent application publication No. 2000-254817 discloses a miter saw having detecting means for detecting the inclination angle of a rotary face of a circular saw relative to a base, and a display for displaying the angle detected by this detecting means.
The miter saw disclosed in Japanese unexamined patent application publication No. 2000-254817 has a detection shaft coupled with the rotating shaft that supports the rotary face of the circular saw and detects the rotation angle of the detection shaft. Hence, the miter saw detects the rotation angle by counting the rotation angle of the detection shaft using a rotary encoder, for example, and displays this detected rotation angle.
The miter saw described above detects the inclination angle for the rotary face of the circular saw relative to the top surface of the base and displays this detected angle on the display, enabling the user to know the current inclination angle instantaneously. However, the displayed inclination angle is always detected based on an initial reference position. The rotation angle of the turntable with respect to the base is similarly always detected and displayed based on an initial reference position.
Usually, the miter saw is configured so that a portion of the base or turntable mechanically engages with the supporting unit to fix the circular saw. Therefore, the saw's sides can form a right angle to the top surface of the base, the most frequently used position, or form an inclination angle of 45° to the top surface of the base, the second most commonly used position.
The miter saw is further configured such that the base and a portion of the turntable engage together mechanically to fix the rotational position of the turntable with respect to the base. Therefore, the side surfaces of the circular saw blade can form a right angle to the contact surface of the fence, the most commonly used position, or form a rotation angle of 15°, 30°, 45°, or 60° with the contact surface of the fence, the next most commonly used positions.
Further, even when a display is provided for displaying the detected angles, the display may not always be used due to malfunctions, various working conditions, or the user's preference. Hence, a graduated scale is also often provided along with the supporting unit or base for indicating commonly used inclination angles and rotation angles as well as the display.
In the miter saw having the above construction, the inclination angle and rotation angle is always detected based on a preset reference point. Therefore, the angle displayed on the display often deviates from the angle determined by a mechanical engagement at a predetermined position or an angle indicated by the graduated scale due to errors in detection or imprecision in the dimensions of the miter saw.
For example, in a miter saw having a maximum inclination range of 45°, the display may show 44° or 46° although the user has tilted the supporting unit to 45°. Further, when the base and turntable are mechanically engaged at such predetermined angles as 15°, 30°, 45°, or 60°, the display may show a different angle from these settings. When this happens, the user is provided with multiple values for the angle, inviting confusion that may lead to a decline in working efficiency.
Further, even when the supporting unit is mechanically engaged with the base or turntable at a predetermined position, vibrations or other external forces may cause the angle displayed on the display to change undesirably.
If the angles of inclination and rotation are detected over a broad range, errors in the detected angle may be large, since the angles are always detected bated on a preset reference position. Hence, it is difficult to display accurate angles of inclination and rotation.